Vehicle traction control system testing is important to confirm anti-lock brake and traction control system performance. Performing low friction coefficient tests under actual road conditions is less than satisfactory for several significant reasons. The remote location of most test sites does not facilitate the provision of an adequate level of engineering and physical support. The variability of test conditions and driver performance increases the difficulty of data evaluation and possibly masks important incremental traction control performance changes. In addition to these problems, winter conditions are available only during a limited portion of each year; and access to areas having suitable conditions is often inconvenient. Testing done at warm climate proving grounds using specially prepared surfaces is inadequate because the coefficient of friction is too high and is generally not controllable.
In attempting to solve the above problems, various apparatuses for dynamically testing a vehicle have been designed. For example, U.S. Pat. No. 4,825,690, issued to Mears on May 2, 1989 discloses a method for controlling a dynamometer to more accurately simulate on-road vehicle operation. A power absorption and motoring unit is typically connected to the powertrain of the vehicle by rotatable rollers upon which vehicle wheels rest or by direct connections to the output shaft of a vehicle engine and transmission to simulate road operating forces. Force and speed transducers measure the force and speed of the power absorption and motoring unit at intervals so that changes in the force produced by changes in vehicle power can be determined. A feed-forward force necessary to bring the power absorption and motoring unit force to a level required to maintain vehicle acceleration and speed at road equivalency is determined, and the power absorption and motoring unit is adjusted to produce the determined force. The feed-forward force includes a factor that compensates for speed-matching errors resulting from large differences between the effective masses of the vehicle and the dynamometer.
U.S. Pat. No. 4,621,524, issued to von Thun on Nov. 11, 1986 discloses a circuit layout for the simulation of moments of inertia of a vehicle on a test stand. The circuit and an associated process utilize a test stand and a test vehicle elastically joined to represent an n-mass oscillator. An m number of additional masses are imitated by means of electronic functional elements so that regulation of the technical structure corresponds to a differential equation system of a (n+m) mass system. An airgap, moment-controlled, electric machine is used as a transmission element between the electronic functional elements and mechanical masses. Vehicle inertial moments are simulated by setting time constraints and amplification factors of the electronic functional elements. Vehicle vibration behavior (natural frequency and attenuation) can also be imitated by the electronic functional elements.
Great Britain Patent No. 1,281,821, issued to Pagdin and Forster and published on Jul. 19, 1972, discloses a method and apparatus for measuring output characteristics of a rotary moving part. The method includes imparting the rotation of the part to a rotary inertia means and generating a series of primary frequency signals representative of the angular displacement of the rotary inertial means. Groups of primary signals are generated at various times and input to a computer, which arithmetically derives a characteristic to be determined.
While each of the above apparatus functions with a certain degree of efficiency, none discloses the advantages of the improved traction control road simulator of the present invention as is hereinafter more fully described.